Centric and centerless grinders with magnetic workrests



-April 30, 1957 Filed Oct. 10,- 1955 e. CROMPTON, J R 2,790,274

CENTRIC AND CENTERLESS GRINDERS WITH MAGNETIC WORKRESTS ,2 Sheets-Sheet 1 INVENTOR April 30, 1957 GQCROMPTON, R 2,790,274

CENTRIC AND CENTERLESS GRINDERS WITH MAGNETIC WORKRESTS Filed Oct. 10, 1955 2 Sheets-Sheet 2 INVENTOR' United States Patent CENTRIC AND CENTERLESS GRINDERS WITH MAGNETIC WORKREST S George Crompton, Jr., Framingham Center, Mass, assignor to Norton Company, Worcester, Mass, a corporation of Massachusetts Application October 10, 1955, Serial No. 539,312

4 Claims. (Cl. 51-103) This invention relates to centric grinders which can be defined as grinders for grinding a surface of revolution on a work piece which is held in position by one or more workrests and whose rotation is controlled by the lateral engagement of a side or sides of said workpiece by a rotating member.

Examples of centric grinders are disclosed in the following U. S. patents:

C. H. Norton, No. 1,779,779, October 28, 1930 J. R. Dunham, No. 1,999,320, April 30, 1935 J. R. Dunham, No. 1,999,321, April 30, 1935 Norton and Belden, No.'2,059,895, November 3, 1936 F. J. Theler, No. 2,249,065, July 15, 1941 Binns and Haas, No. 2,478,562, August 9, 1949 Theler and Mehlhope, No. 2,478,607, August 9, 1949 F. S. Haas, No. 2,641,873, June 16, 1953 H. E. Balsiger, No. 2,694,883, November 23, 1954 One object of the invention is to provide a workrest for centric grinders, or for other grinders such as centerless grinders, which exerts a force attracting the workpiece towards the rest. Another object is to provide such a workrest which applies a frictional retarding force to rotation of the workpiece, for example aiding the work plate or chuck in resisting the driving force of the grinding wheel which tends to rotate the workpiece. In this connection it is pointed out that in centric as well as in centerless grinders, the face plate on the one hand or the regulating wheel on the other hand is erroneously stated to rotate the work during grinding because the grinding wheel is trying to rotate the workpiece at a greater speed than is permitted by the face plate on the one hand or the regulating wheel on the other hand. However, before the grinding wheel engages the workpiece, the rotating face plate on the one hand and the regulating wheel on the other hand does function to rotate the workpiece. Another object of the invention is to prevent rotation of the workpiece faster than the face plate or the regulating wheel, that is to say at greater angular velocity than the former or at greater peripheral velocity than the latter. Another object is to provide a workrest of the type indicated which is simple to construct, reliable in operation and is always active providing the attracting force. Another object is to provide a workrest of such construction that a pair of them can readily be fitted into the space available in a centric grinder. Another object is to provide a workrest of such construction that a single one or two or more in tandem can readily be provided in the space available in a centerless grinder. Another object is to provide workrests which will hold workpieces firmly in grinding position.

Other objects will be in out hereinafter.

In the accompanying drawings illustrating one of many possible embodiments of the workrest according to the invention,

Figure 1 is a view partly in end elevation and partly part obvious or in part pointed 2,790,274 Patented Apr. 30, 1957 in section of the elements of a centric grinder including a pair of the workrests,

Figure 2 is a plan view, looking radially outward from the center of the workpiece, of one of the workrests,

Figure 3 is a radial sectional view through the mounting ring showing one of the workrests in elevation,

Figure 4 is an enlarged sectional view taken along the line 4-4 of Figure 3,

Figure 5 is a view similar to Figure 1 showing a centerless grinder equipped with the workrest of the invention.

Referring now to Figure 1, the centric grinder provides a grinding wheel 10 mounted and rotated in any usual or desired manner, and positioned and fed by any suitable infeed mechanism. The centric grinder also provides a rotatable face plate 11 which may be a magnetic chuck and is shown as annular in form. The grinding wheel 10 and the face plate 11 rotate in the direction of the arrows shown but the grinding wheel 10 rotates much faster peripherally. The face plate 11 can be rotated in any conventional or suitable manner.

Referring now to Figure 3, a portion of the headstock of the machine which rotatably supports the face plate 11 is indicated at 12. To this portion 12 is secured by means of bolts 13 shown in Figure 1 a mounting ring 14 shown in Figures 1 and 3 having arcuate T-slots 15, 16

and 17. The T-slot 17 is located in an inwardly projecting portion 18 of the mounting ring 14.

I provide box halves 20 made of some non-magnetic material such as brass each one having a tail portion 21 with a slot 22 therein and each one having a lateral portion 23 with a slot 24 therein. T-bolts 25 through the slots 22 and into the T-slots 15 and 16 with nuts 26 thereon serve to hold the tail portions 21 on the mounting ring 14 and it will be seen that a wide range of adjustment is provided. Similarly T-bolts 27 with nuts 28 extending through the slots 24 and into the T-slot 17 hold the lateral portions 23 and in this case also a wide range of adjustment is provided. These adjustments can be made radially to accommodate diiferent sizes of workpieces and angularly to receive the different resultant forces of different grinding conditions.

I provide box halves 30 which may be made of nonmagnetic material such as brass and these are secured to the box halves 20 by means of screws 31 extending into threaded holes 32 in the box halves 20. By nonmagnetic I mean not only that the box parts 20 and 30 are not magnetized but also that they are poor conductors of magnetic lines of force, that is to say they do not short-circuit a magnetic field although as well known magnetic force cannot be completely insulated.

In each box comprising the parts 20 and 30 I provide powerful magnets are made of an alloy of aluminum,

nickel and cobalt, sometimes referred to by the trade-- mark Alnico, and I prefer to use such powerful magnets. As magnets are readily available on the market I need not further describe the composition nor the manufacture thereof. These bar magnets 40 and 41 are magnetically connected at the end remote from the workpiece 45 by yokes 46 of any highly permeable material such as soft iron, wherefore a pair of bar magnets 40 and 41 and a yoke become a horseshoe magnet. Bar magnets 40 and 41 are magnetically and mechanically separated by means of a separator 48 of material of low permeability such as brass, but other non-ferrous metals and even plastics could be used.

Each bar magnet 40 and 41 is provided with a pole piece 50 and 51 respectively separated by a wear resistant piece 52 which is preferably made of boron carbide,

134C, or any other formula, which is readily available shapes such as that of the wear resistant piece 52 are easy to mold out of boron carbide. As illustrated herein and in order to fit in the end of the box 2030 which it will be seen is open at the inner end, the piece 52 can be a rectangular parallelepiped modified by an arcuate surface where it contacts the workpiece. This arcuate surface need not be cylindrical as for some shapes of workpieces other surfaces of revolution would be desired. The workpiece 45 can be any style round workpiece but centric grinders are much used to grind the inner race as well as the outer race of ball bearings but so far as this invention is concerned the grinding wheel may have a straight face or an arcuate face to grind a groove or it might even be an internal grinding wheel to grind the internal circumference of the workpiece either to produce thereon a cylindrical surface or a grooved surface. Also the exterior of the workpiece might with the use of the workrest of my invention be ground to a tapered or conical surface as clearly my invention has no limitation in any of these respects.

In place of boron carbide other hard wear resistant materials might be used for the wear resistant piece 52. Examples are sintered alumina and other ceramics and also the carbides such as tungsten carbide bonded with cobalt. Cobalt is a permeable metal but of low permeability compared to iron, and the commercial hard carbides such as tungsten carbide with or without titanium carbide and tantalum carbideare bonded (cemented) with cobalt, but the amount of cobalt in these compositions is so small that they can be used in this invention for the pieces 52.

Illustratively I stated that the yoke 46 and pole pieces 50 and 51 can be made of soft iron. This includes c ld rolled steel, an easily machinable magnetically highly permeable but also a strong material. Compositions to make powerful magnets such as the Alnico composition hereinbefore referred to are weak and brittle and they readily chip. Therefore it is advantageous to provide separate pole pieces 55) and 51 made of cold rolled steel or the like which is highly permeable but strong and will not chip. Such highly permeable material carries the magnetic lines of force with little resistance. However, in some cases, especially where the magnets are made of hard steel as used to be the case, the magnets may directly contact the workpiece. Again another advantage of having separate pole pieces is that most of the heat produced by friction is dissipated before it reaches the magnets thus preventing damage to the magnets by heating. The relative advantages will be weighed in given cases and it is noted that in some cases it will be desired to limit the magnetic attraction as if it were too powerful it would stop the face plate 11 from turning the workpiece 45 prior to engagement thereof by the grinding wheel 10. It is desirable that the workpiece be rotating when the grinding wheelfirs-t engages it as is known in the art.

The magnetic circuit is completed through the workpiece 45 which is assumed to be made of steel or other ferrous metal which is attracted by a magnet as is usually the case. Thereby the workpiece is attracted to the workrest and the force is right along the center line of the workrest, in this case in the direction of the center line of the separating piece 48. Thus the objects of the invention are achieved and workpieces are held securely in grinding position. My magnetic workrests assist in locating fresh workpieces in grinding position in automatic machines having feeding and discharging mechanism to introduce and to remove workpieces such as described in some of the patents listed hereinbefore.

The wear resistant pieces 52 made of boron carbide or otherwise prevent too rapid wear of the pole pieces 56 and 51 or of the magnets 40 and 41. In some cases, however, it may be desirable to make the pole pieces 59 and 51 out of hard steel where some diminution of the magnetic force can be tolerated or is even wanted for reasons stated above. wear resistant pieces 52 might be omitted altogether relying upon the pole pieces 50 and 51 or even the magnets themselves to take the wear. In this connection it will be readily seen that not only are the rests easily adjusted to accommodate for Wear but also the entire contents of the boxes 2039 or any part thereof can easily be replaced. These boxes securely clamp the various parts together when in use.

By reason of the fact that the magnets 40 and 41 and the separator 43 are clamped together by the joinder of the two halves 20 and 30 of the box and that as shown there is clearance between the box halves, the parts do not have to be made to very close tolerances which is a good manufacturing advantage. This clamping action insures that the pole pieces 50 and 51 and the Wear resistant piece 52 will be securely locked in position and further that there is good contact between the yoke 46 and the magnets 40 and 41 as well as between the pole pieces 50 and 51 and the magnets.

As previously indicated, the workrest can be used in centerless grinders as well as in centric grinders. A centerless grinder, Figure 5, has a regulating wheel 60 sometimes called a control wheel which acts like the face plate of a centric grinder in that it controls rotation of the workpiece, that is to say prevents it from attaining a peripheral velocity higher than itself by supplying a braking force thereto frictionally to retard it from being over-driven by the grinding wheel and it also, the same as the face plate of a centric grinder, sets the workpiece in rotation at a slow speed prior to its engagement by the grinding wheel. Thus the face plate 11 is a species of control wheel.

The wear resistant piece is preferably of low magnetic permeability and is made of hard material examples of which have been given. However, the wear could be taken by a pair of pieces of hard steel outside of the magnetic poles which would not short-circuit the magnetic field. The magnetic workrests set up magnetic fields in the locus of a workpiece in position to be ground by the grinding wheel and to be controlled by the control wheel.

It will thus be seen that there has been provided by this invention a workrest for centric grinders in which the various objects hereinabove set forth together with many thoroughly practical advantages are successfully achieved. As many possible embodiments may be made of the above invention and as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth or shown in the accompanying drawings is to be interpreted as illustrative and not in a limiting sense.

I claim:

1. A grinder comprising a grinding wheel mounted for rotation, rotatable work piece engaging means positioned to rotate said work piece, a workrest comprising a pair of bar magnets arranged in parallel relation and with opposite poles adjacent each other, a separator of low magnetic permeability separating said magnets, a yoke of high magnetic permeability in engagement with one pair of opposite poles, clamping means for clamping said magnets together, second magnetic poles of opposite polarity at the ends of said magnets remote from said one pair of opposite poles that are in engagement with said yoke, and mounting apparatus to mount said workrest in said grinder for engagement with the periphery of a workpiece mounted for grinding therein.

2. A centric grinder according to claim l in which the magnetic workrest comprises a permanent magnet.

3. A centerless grinder comprising a grinding wheel mounted for rotation, a control wheel mounted for rotation adjacent saidv grinding wheel and in position to engage a workpiece that is in position to be ground by said grinding wheel and thereby to control the rotation of said workpiece to prevent it from rotating at the peripheral speed of the grinding wheel, and a workrest mounted In some cases the intervening to engage the periphery of and to hold a workpiece in position to be ground by said grinding wheel and to be engaged by said control wheel, said workrest being a magnetic workrest and setting up a magnetic field in the locus of a workpiece in position to be ground by said grinding wheel and to be controlled by said control Wheel, said workrest comprising a pair of bar magnets arranged in parallel relation and with opposite poles adjacent each other, a separator of low magnetic permeability separating said magnets, a yoke of high magnetic permeability in engagement with one pair of opposite poles, clamping means for clamping said magnets together, and second magnetic poles of opposite polarity at the ends of said magnets remote from said one pair of opposite poles that are in engagement with said yoke.

4. A centerless grinder according to claim 3 in which the magnetic workrest comprises a permanent magnet.

References Cited in the file of this patent UNITED STATES PATENTS 2,063,939 Lott Dec. 15, 1936 2,187,240 Karasick Jan. 16, 1940 2,269,149 Edgar Jan. 6, 1942 2,383,008 Meister Aug. 21, 1945 2,405,773 Barrett Aug. 13, 1946 2,478,562 Binns et a1. Aug. 9, 1949 2,478,607 Theler et a1. Aug. 9, 1949 2,581,226 Arnold Jan. 1, 1952 

